Fallback transport

I have two location profiles. One where the SMTP server is
connect'able and the other where a direct connection to the SMTP
server is not available. The direct connection times out.

In the first location, everything works fine. But in the second
location, mail keeps waiting until I move to the first location when
EXIM gets a direct connection to the SMTP server.

In the second location, what I want to do is to tunnel the connection
to the SMTP server through say port XXX on the localhost. But this
tunneling should be used only when there is no direct connection to
the SMTP server. Thus this is the fallback option. But the problem is
that the fallback hosts do not allow port numbers to be specified.

Has anybody done a similar thing earlier ?

I using EXIM 3.34 on Debian.